You just got back from a great jog, sat down for a while -- then stood up and felt like you are going to faint. Or maybe you simply jumped out of bed when the alarm went off and felt lightheaded or you stood up quickly to answer the phone and felt, well, weird. Or you ate a big dinner and felt momentarily weak when you stood up to leave the restaurant.

What’s going on here - and is it serious?

Most everyone is aware of how high blood pressure (hypertension) is a potential health problem but we rarely hear about low blood pressure, which can cause the symptoms described above. While it is rarely a serious threat to health, low blood pressure affects many people of all ages from time to time – and it can make you faint or feel just plain lousy.

Synergy went to Emory’s Executive Health program internist Sharon Bergquist, MD, an Assistant Professor of Medicine at Emory University’s Division of General Medicine and Geriatrics, to learn the cause of low blood pressure symptoms and find out what to do about them.

The low down on low blood pressure

Every time your heart beats, it pumps out blood into the arteries. The force of your blood pushing against the walls of your arteries is measured as your blood pressure. It’s highest when your heart beats to pump blood out, resulting in the systolic pressure (recorded as the first number in a blood pressure reading). When your heart is at rest between beats, the blood pressure falls and is noted as the diastolic pressure (the second number in a blood pressure reading).

According to the National Institutes of Health, some people have lower than normal blood pressure all the time, although they feel fine and their readings are normal for them. In other people, symptoms of low blood pressure are worrisome.

“Blood pressure is too low when it causes symptoms or problems. That number can be different from person to person. As a general rule of thumb, readings under 90/60 are in the range where they may cause symptoms of hypotension, or low blood pressure,” Dr. Bergquist tells Synergy.

How does a person feel if their low blood pressure is troublesome? “The most common symptom of hypotension is lightheadedness, followed by fatigue. Some people also feel nausea,” Dr. Bergquist answers.

Common causes of low blood pressure

The most common cause of hypotension is dehydration. “This can occur simply from not drinking adequate fluids or from losing excessive fluids through sweat, vomit, or diarrhea,” Dr. Bergquist explains.

Why do some people feel a little – or a lot – “lightheaded” and even faint after standing up very quickly? “The degree to which you feel symptoms from standing up quickly depends on how well your body can take counter measures against the drop in blood pressure,” Dr. Bergquist tells Synergy. “If your body is able to quickly raise your heart rate and narrow your blood vessels to raise your blood pressure, lightheadedness will be mild and may even go unnoticed. If you are dehydrated or have a medical condition that affects your heart or nervous system, you may feel faint or even pass out.”For some people, jumping out of bed when the alarm goes off in the morning can make them experience lightheadedness, too. “Getting out of bed is a common time to experience low blood pressure. This is due to the rapid change from lying down to standing and the dehydration that develops overnight,” Dr. Bergquist explains.

She also points out that blood pressure can transiently drop and make you feel momentarily faint after eating. “After a large meal, blood is directed to the stomach and digestive system. That causes a drop in blood pressure, called postprandial hypotension, similar to standing up quickly,” Dr. Bergquist says. “Postprandial hypotension is common and can be avoided by eating small meals, avoiding rapidly processed carbohydrates (white flour and white sugar products) that rapidly move from the stomach to the small intestines, drinking lots of fluids, and avoiding diuretics such as alcohol and caffeine.”

On the other hand, not eating can also cause a drop in blood pressure. “By skipping a meal, you may feel faint from missing the opportunity to hydrate through food and from the drop in blood sugar,” she adds.

Dr. Bergquist points out that while blood pressure can produce symptoms in people of any age, it is more common in older people. “As people age, they are more at risk for hypotension because their ability to respond to a drop in blood pressure is slower. When a person changes position quickly, blood pools to the legs and away from the brain. The body responds by raising heart rate and clamping down blood vessels to restore blood pressure. As a person gets older, nerves, pressure receptors in blood vessels and stiffer arteries respond slower to a drop in blood pressure, resulting in hypotension.”

When to see your healthcare provider

If you’ve started or changed any medications, that could be the source of new low blood pressure symptoms - and it’s something to discuss with your doctor. “The biggest offenders are blood pressure medications. They can slow your heart rate and block blood vessels from narrowing to restore blood pressure,” Dr. Bergquist says. “Medications for erectile dysfunction, Parkinson’s disease and antidepressants can also cause hypotension.”

While low blood pressure is often harmless, it can be an important warning sign. “If symptoms from low blood pressure last more than seconds or minutes, occur frequently, or include faintness or passing out, they can be a sign of a serious problem. Such problems include diabetes, heart disease, Parkinson’s disease, thyroid disease or anemia,” Dr. Bergquist says. “If your symptoms last more than seconds or minutes, occur frequently, or cause faintness, you should see your physician.”